International Journal of Reliability, Quality and Safety Engineering

As the Internet technology has developed, the demands for the improvement of the reliability and security of the system connected with the Internet have increased. Although various services are performed on the Internet, illegal access on the Internet has become a problem in recent years. This paper formulates stochastic models for a system with illegal access. The server has the function of IDS, and illegal access is checked in multiple stages which consist of simple check, detailed check and dynamic check. We apply the theory of Markov renewal processes to a system with illegal access, and derive the mean time and the expected checking number until a server system becomes faulty. Further, optimal policies which minimize the expected cost are discussed. Finally, numerical examples are given.

High-power light emitting diodes (HPLEDs) have been applied extensively in lighting industry. This study proposes a procedure for analyzing the reliability of a typical HPLED assembly of street light under thermal environments. The junction temperature of a single package component under a canonical thermal environment is found through finite element analysis. The lifetime of the package component is then estimated with the help of the life prediction rule after the junction temperature is obtained. To reflect real situation, the uncertainty of thermal environments is further considered by assuming that the mixed convection heat transfer coefficient is a random variable. To simplify the analysis of the assembly, the circuit configuration of the assembly is addressed and discussed from the viewpoint of a system and its components. It is found that uncertainty of thermal environments does make the lifetime distributions more dispersed. With regard to the reliability, the assembly degrades faster than that of its package components; however, the reliability distribution of assembly is more concentrated than that of its package components. The results of this study can provide information for a street-light engineer to plan a maintenance strategy in advance.

Testing life cycle poses a problem of achieving a high level of software reliability while achieving an optimal release time for the software. To enhance the reliability of the software, retain the market potential for the software and reduce the testing cost, the enterprise needs to know when to release the software and when to stop testing. To achieve this, enterprises usually release their product earlier in market and then release patches subsequently. Software patching is a process through which enterprises debug, update, or enhance their software. Software patching when used as a debugging process ensures an optimal release for the product, increasing the reliability of the software while reducing the economic overhead of testing. Today, due to the diverse and distributed nature of software, its journey in the market is dynamic, making patching an inherent aspect of testing. A patch is a piece of software designed to update a computer program or its supporting data to fix or improve it. Researchers have worked in the field to minimize the testing cost, but so far, reliability has not been considered in the models for optimal time scheduling using patching. In this paper, we discuss reliability, which is a major attribute of the quality of software. Thus, to address the issues of testing cost, release time of software, and a desirable reliability level, we propose a reliability growth model implementing software patching to make the software system reliable and cost effective. The numeric illustration has been implemented using real-life software failure data set.

This paper attempts to model the reliability of dynamic k-out-of-n systems with component partnership (DKNCP) in which a mixture of deteriorating components and multiple types of shocks are inflicted on the system. Previous studies were merely focused on the DKNCP systems affected by one type of shock that influenced all its components. In practice, however, shocks do not necessarily affect all the components. Hence, shocks may be classified based on their magnitude, specifications, and the components they affect. In this paper, random shocks are classified into distinct sets based on the components affected. DKNCP or adaptive KNCP is a new redundancy system that can be applied when a specific number of high-performance components is required which cannot be replaced by lower-performance components even if the number of these components is high. In a DKNCP system, the components contribute to the system operation in different ways and can make partnership groups for the system to survive when a component failure occurs. Also, we consider two failure mechanisms: accumulating degradation and random shocks. Two types of random shocks are also considered in the model: critical shocks, that cause instantaneous component failure, and non-critical ones, that increase natural degradation by a random amount.

This paper develops a Monte Carlo Simulation (MCS) approach to estimate the performance of a multistate manufacturing network (MMN) with joint buffers. In the MMN, products are allowed to be produced by two production lines with the same function to satisfy demand. A performance index, system reliability, is applied to estimate the probability that all workstations provide sufficient capacity to satisfy a specified demand and buffers possess adequate storage. The joint buffers with finite storage are considered in the MMN. That is, extra work-in-process output from different production lines can be stored in the same buffer. An MCS algorithm is proposed to generate the capacity state and to check the storage usage of buffers to evaluate whether the demand can be satisfied or not. System reliability of the MMN is estimated through this MCS algorithm. Besides, performability for demand pairs assigned to production lines can be obtained. A practical example of touch panel manufacturing system is used to demonstrate the applicability of the MCS approach. Experimental result shows that system reliability is overestimated when buffer storage is assumed to be infinite. Moreover, joint buffer for an MMN is more reliable than buffers are installed separately in different production lines.